Allen-Bradley 1756 ControlLogix Modules – 1756-PAR2

Technical Dossier

Product Details And Specifications

Allen-Bradley 1756 ControlLogix Series Technical Notes

The Allen-Bradley 1756 ControlLogix platform is one of the most widely deployed programmable automation controller (PAC) architectures in global heavy industry. Installed across petrochemical refineries, nuclear power generation facilities, offshore oil & gas platforms, pulp and paper mills, and large-scale water treatment infrastructure, the 1756 series represents Rockwell Automation's flagship control tier. Its modular backplane architecture supports mixed I/O, redundant CPU configurations, and deterministic real-time communication via ControlNet, EtherNet/IP, and DeviceNet. The platform's scalability — from 4-slot to 17-slot chassis — makes it the reference standard for safety-critical and high-availability process control environments worldwide.

The Evolution of 1756 ControlLogix Architecture

The ControlLogix platform was introduced in the mid-1990s as a successor to the PLC-5 and SLC 500 families, designed to address the growing demand for multi-discipline control within a single chassis. The original 1756-L1 and 1756-L20 controllers established the Logix5000 firmware baseline. Subsequent generations introduced the 1756-L6x series with expanded memory and faster scan rates, followed by the 1756-L7x series featuring integrated USB programming ports, SD card firmware storage, and enhanced EtherNet/IP throughput. The current 1756-L8x generation adds 64-bit processing, CIP Security, and native integration with FactoryTalk Logix Echo for virtual controller emulation. Compatibility across generations is managed through firmware revision alignment; older 1756-A4, 1756-A7, and 1756-A10 chassis remain electrically compatible with modern modules, though mixed-generation deployments require careful firmware and SERCOS/ControlNet bridge management. Power supply compatibility is a critical consideration: the 1756-PAR2 redundant power supply bundle is specifically designed to maintain uninterrupted backplane power in high-availability chassis configurations.

1756 ControlLogix Full Catalog & Functionalities (SKU List)

Controllers (CPU Modules)

• 1756-L71: Logix5571 controller, 2MB memory, standard ControlLogix CPU
• 1756-L72: Logix5572 controller, 4MB memory, dual Ethernet ports
• 1756-L73: Logix5573 controller, 8MB memory, high-capacity process control
• 1756-L74: Logix5574 controller, 16MB memory, large-scale system CPU
• 1756-L75: Logix5575 controller, 32MB memory, maximum L7x series capacity
• 1756-L83E: Logix5583E controller, 40MB memory, L8x generation, CIP Security
• 1756-L85E: Logix5585E controller, 40MB memory, highest L8x performance tier

Power Supply Modules

• 1756-PA72: 120/240VAC input power supply, 13A backplane output
• 1756-PB72: 18-32VDC input power supply, 13A backplane output
• 1756-PA75R: Redundant 120/240VAC power supply, right-side chassis mount
• 1756-PB75R: Redundant 18-32VDC power supply, right-side chassis mount
• 1756-PAR2: Redundant AC power supply bundle — paired redundant power assembly for uninterrupted backplane supply in critical chassis; includes primary and secondary supply modules with automatic failover

Digital I/O Modules

• 1756-IB16: 16-point 24VDC digital input module, sourcing
• 1756-OB16E: 16-point 24VDC digital output module, electronically fused
• 1756-IA16: 16-point 120VAC digital input module
• 1756-OA16: 16-point 120VAC digital output module

Analog I/O Modules

• 1756-IF16: 16-channel analog input, 4–20mA / 0–10V, high-density
• 1756-OF8: 8-channel analog output, voltage and current configurable
• 1756-IF8: 8-channel analog input, differential, 16-bit resolution

Communication & Network Adapter Modules

• 1756-EN2T: EtherNet/IP communication module, single copper port, 100Mbps
• 1756-EN2TR: EtherNet/IP module with dual-port DLR ring topology support
• 1756-CN2R: ControlNet redundant media communication module
• 1756-DNB: DeviceNet scanner bridge module for legacy device integration

Chassis

• 1756-A4: 4-slot ControlLogix chassis
• 1756-A7: 7-slot ControlLogix chassis
• 1756-A10: 10-slot ControlLogix chassis
• 1756-A13: 13-slot ControlLogix chassis
• 1756-A17: 17-slot ControlLogix chassis, maximum capacity

Quality Control for the 1756 ControlLogix Range

The 1756 platform's backplane operates on a proprietary high-speed serial bus; module integrity testing requires chassis-level communication verification, not only standalone bench testing. DriveKNMS applies a multi-stage QC protocol for all 1756 series units: (1) visual inspection for capacitor degradation, connector pin condition, and PCB contamination; (2) powered backplane insertion test using a reference 1756-A7 chassis with known-good CPU; (3) firmware revision verification and Logix5000 communication handshake confirmation; (4) for power supply modules including the 1756-PAR2, load bank testing at rated backplane current with redundancy failover simulation; (5) 48-hour burn-in cycle under thermal cycling conditions. Modules passing all stages are issued a DriveKNMS test certificate with serial number, firmware revision, and test date recorded.